1. Field of the Invention
The present invention relates to a power transmission member for an electric power steering system. More specifically, the present invention relates to a power transmission member for an electric power steering system that can more effectively reduce noise caused by the clearance between inner and outer rotors, compared with a power transmission member in the related art, and can prevent noise caused by collision and vibration at the portion to which a driving shaft and a driven shaft are coupled while transmitting power.
2. Description of the Prior Art
A steering apparatus for a vehicle is an apparatus for allowing a driver to freely change the progress direction of the vehicle by rotating the steering wheel. The steering apparatus arbitrarily changes the center of rotation about which the vehicle's front wheels turn to assist the driver to drive the vehicle in a desired direction. The steering apparatus uses a power steering system as an auxiliary power mechanism in order to reduce the driver's force. A power steering system is broadly divided into a hydraulic power steering system that uses hydraulic pressure that assists with a steering force by operating a hydraulic pump using the force of an engine and an electric power steering system that uses an electric motor.
A hydraulic power steering system assists with a driver's steering force by detecting the rotation of a steering wheel, operating a hydraulic pump using a rotational force transmitted from an engine, and transmitting hydraulic pressure to a driving unit, such as a cylinder, which is provided on a rack bar or a steering column.
An electric power steering system enables a steering apparatus to effectively operate by detecting the rotation of a steering wheel and operating a motor that is installed on a rack or a steering column to assist with a rotary motion. An electric power steering system is divided into a rack assist type electric power steering system (R-EPS) and a column type electric power steering system (C-EPS).
FIG. 1 is a schematic view of an electric power steering system in the related art.
As illustrated in FIG. 1, the electric power steering system includes a steering system 100 that extends from a steering wheel 101 to wheels 108 and an auxiliary power device 120 that provides auxiliary steering power for the steering system 100.
The steering system 100 includes a steering column 102 that is connected, at one side thereof, to the steering wheel 101 to rotate together with the steering wheel 101 and is connected, at the opposite side thereof, to a pinion shaft 104 through a pair of universal joints 103. The pinion shaft 104 is connected to a rack bar through a rack-pinion mechanism 105, and the opposite ends of the rack bar are connected to the wheels 108 of the vehicle through tie rods 106 and knuckle arms 107. The rack-pinion mechanism 105 is constituted by a pinion gear 111 and a rack gear 112 that are engaged with each other, in which the pinion gear 111 is formed on the pinion shaft 104 and the rack gear 112 is formed on one side of the outer circumferential surface of the rack bar. When a driver operates the steering wheel 101, a torque is generated in the steering system 100, and the wheels 108 are turned by the torque through the rack-pinion mechanism 105 and the tie rods 106.
The auxiliary power device 120 includes: a torque sensor 125 that senses the torque applied to the steering wheel 101 by a driver and outputs an electrical signal proportional to the detected torque; an electronic control unit (ECU) 123 that generates a control signal on the basis of the electrical signal transmitted from the torque sensor; a motor 130 that generates auxiliary power on the basis of the signal transmitted from the electronic control unit 123; and a speed reducer 140 that transmits the auxiliary power generated by the motor to the steering column 102.
FIG. 2 is a partially sectioned view illustrating a power transmission member of the electric power steering system in the related art.
As illustrated in FIG. 2, the power transmission member of the electric power steering system includes a motor 130, a driving shaft 205, an inner rotor 220, an outer rotor 215, a resilient body 210, a first bearing 250, a worm shaft 235, a worm gear 245, a second bearing 270, a compression screw 255, a compression spring 265, and a gear housing 260.
The motor 130 has the driving shaft 205 that extends from the motor housing to the outside, and the outer rotor 215 has an empty space therein and is connected, at one side thereof, with the driving shaft 215 to operate in conjunction with the driving shaft 215. The first and second bearings 250 and 270 fix the worm gear 245 such that the worm gear 245 is directed toward the worm wheel gear 240 installed on the steering column. The compression spring 265 supports the worm gear 245 toward the worm wheel gear 240 through the compression screw 255 and supports the second bearing 270. Accordingly, when the compression screw 255 is tightened, the compression screw 255 moves to compress the compression spring 265 such that the worm gear 245 may be firmly engaged with the worm wheel gear 240 by the compressive force of the compression spring 265.
The inner rotor 220 is connected to the worm shaft 235 and is inserted into the outer rotor 215 that is connected with the driving shaft 205 at one side thereof.
However, since the power transmission member of the electric power steering system in the related art has a structure in which the inner rotor is coupled to the outer rotor through simple press-fit and makes direct contact with the inside of the outer rotor, a large impact is inversely input through the steering column to cause the wear of the clearance and to cause noise that is due to contact when the vehicle is aging or traveling on a road, such as an off-road.
Furthermore, a process of assembling the inner rotor and the outer rotor and a process of applying grease to the space therebetween are required, which causes an increase in the assembly process and cost.